When a power supply system is constructed, in addition to a further expansion of a power distribution grid in a more stable way, a main issue has been providing such a system with a capability of introducing a large amount of natural energy. A power network system called Digital Grid (registered trademark) has been proposed as a new power network (see Patent literature 1 and Non-patent literature 1). Digital Grid (registered trademark) is a power network system in which a power network is partitioned into small-sized cells and these cells are asynchronously interconnected. Each power cell may be small (e.g., a house, a building, or a commercial facility) or may be large (e.g., a prefecture or a municipality). Each power cell naturally includes a load, and may also include a power generation facility or a power storage system. The power generation facility may be, as an example, a power generation facility that uses natural energy generated by, for example, photovoltaic power, wind power, and geothermal power.
In order to freely generate power inside each power cell and to further smoothly interchange power among the power cells, the power cells are asynchronously connected. (That is, even when the plurality of power cells are interconnected, a frequency, a phase, and a voltage of power used in each power cell are asynchronous with those used in other power cells.) FIG. 71 shows an example of a power network system 10.
In FIG. 71, a utility grid 11 sends bulk power from a large-scale power plant 12. A plurality of power cells 21-24 is arranged. Each of the power cells 21-24 includes a load such as a house 31 and a building 32, power generation facilities 33 and 34, and a power storage system 35. The power generation facility may include, as an example, a solar panel 33 and a wind turbine 34. The power storage system is, for example, a storage battery 35. In this specification, the power generation facility and the power storage system may be collectively called a distributed power supply.
Further, the power cells 21-24 respectively include power routers 41-44 which serve as connection ports to be connected to other power cells or the utility grid 11. Each of the power routers 41-44 includes a plurality of legs (LEG). (Due to space constraints, the symbols for the legs are omitted in FIG. 71. It should be interpreted that the white circles attached to the power routers 41-44 are connection terminals of each leg.)
Now, each leg includes a connection terminal and a power conversion unit, and an address is attached to each leg. The power conversion by the leg means converting AC to DC or DC to AC and changing the phase, the frequency, and the voltage of the power.
All the power routers 41-44 are connected to a management server 50 by a communication network 51 and operations of all the power routers 41-44 are integrally controlled by the management server 50. For example, the management server 50 instructs each of the power routers 41-44 to transmit or receive power for each leg using the address attached to each leg. Accordingly, power is interchanged among power cells through the power routers 41-44.
Since power interchange among the power cells is achieved, a plurality of power cells can share, for example, one power generation facility 33 or 34 or one power storage system 35. If an excessive power can be interchanged among the power cells, a supply-demand balance of power can be kept stable while greatly reducing the equipment cost.
Further, Patent Literature 2 discloses a technique related to a power system in which priorities are assigned to a plurality of loads to which power is supplied according to the relative importance among the plurality of loads. In the power system disclosed in Patent Literature 2, for example, when the predicted available power is smaller than the demand of the overall load, the balance between the demand and the supply of the overall power in the system is adjusted by cancelling a connection(s) to the input power source for a load(s) having low importance.